Globular Clusters

We live in a fairly lonely region of the Milky Way galaxy. The nearest star system is more than four light-years away, and only a handful of stars lie within 10 light-years. Partly because of that, only a few bright stars adorn the night sky.

But the night skies in other regions of the galaxy are filled with thousands of bright stars — so many stars that the night never really gets dark.

These regions are known as globular clusters. Most contain a hundred thousand stars or more, and some have populations of more than a million stars. Yet the clusters are only a few dozen light-years across, so the stars are packed many times closer together than in our region of the galaxy.

Astronomers have discovered more than 150 globulars orbiting the center of the Milky Way. Most of them are in the halo — a volume that extends far above and below the galaxy’s flat disk.

The stars in globular clusters are some of the oldest in the galaxy. They formed when the Milky Way was new — more than 10 billion years ago. Any hot, massive stars that were born in the clusters blasted themselves to bits early on. That left only the smaller, more sedate stars, which can shine for billions of years.

These stars make a good laboratory for astronomers to study the early history of the Milky Way. Since the stars formed when the galaxy was young, they preserve a record of its early chemistry.

We’ll talk about one of the brightest globulars tomorrow.

Script by Damond Benningfield, Copyright 2014

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